Applications of surfactants in pharmaceutical dosage forms

To impose a desired effect on the human body, a therapeutically potent substance (drug molecule) must be present in suitable concentration at its target organ. More than 40% of the new pharmacologically potent molecules exhibit poor biopharmaceutical properties, which prevents them from reaching the target organ in a sufficient quantity at the appropriate rate [1]. Those molecules must be formulated (pharmaceutically prepared in their final dosage form) prior to administration as a medicine. The main goals of such formulations are [2] 1. To improve the bioavailability of the drug (to increase the fraction of an administered dose of unchanged drug that reaches the systemic blood circulation) 2. To alter the release rate of the drug 3. To target the drug to a specific organ Much effort is therefore invested in research and development by the pharmaceutical industry in finding the optimal dosage forms for the potent molecules. Surfactants (or amphiphilic molecules) play one of the most important roles in creating the suitable vehicle for drug administration. Amphiphilic molecules consist of at least two parts, hydrophobic tail and hydrophilic head groups. Owing to this structure, interactions of the drug with amphiphilic molecules in pharmaceutical dosage form can significantly alter the solubility, permeability, and dissolution properties of a drug. Thus, surfactants are mostly added to dosage forms as inactive excipients, which improve the bioavailability of the drug. Such improvement can be achieved by [2] 1. Enhancing the aqueous solubility of the drug 2. Prolonging the time that the target tissue is exposed to the drug 3. Improving permeability of the drug through the body’s membranes and barriers Surfactants may also be used for targeting a drug to a specific organ in the body, or for achieving better physical and chemical stability of the dosage form.